In optical communications networks, optical communications modules are used to transmit and/or receive optical signals over optical fibers. Optical receiver modules are optical communications modules that receive optical signals, but do not transmit optical signals. Optical transmitter modules are optical communications modules that transmit optical signals, but do not receive optical signals. Optical transceiver modules are optical communication modules that transmit and receive optical signals. An optical transmitter or transceiver module generates amplitude and/or phase and/or polarization modulated optical signals that represent data, which are then optically coupled, or imaged, onto an end of an optical fiber by an optics system of the module. The light source is typically a laser diode or light emitting diode (LED). The optics system typically includes one or more reflective elements, one or more refractive elements and/or one or more diffractive elements.
An optical receiver or transceiver module includes a photodetector (e.g., a photodiode) that detects an optical data signal transmitted over an optical fiber and converts the optical data signal into an electrical signal, which is then amplified and processed by electrical circuitry of the module to recover the data. An optics system of the module optically couples the optical data signals passing out of the end of the optical fiber onto the photodetector.
While various transceiver and optical fiber link designs enable the overall bandwidth, or data rate, of optical fiber links to be increased, there are limitations on the extent to which currently available technologies can be used to increase the bandwidth of an optical fiber link. It has been shown that receiver-based electronic dispersion compensation (EDC) techniques in combination with particular modulation formats can be used to increase the bandwidth of optical fiber links. It is also known that multiple optical links can be combined to achieve an optical link having a higher data rate than that of each of the individual optical links that form the combination. However, in order to construct such a link, multiple sets of parallel optics and a corresponding number of optical fibers are needed, which significantly adds to the costs associated with such links. Therefore, there is difficulty associated with scaling such links to achieve increasingly higher bandwidths.
Recently, attempts have been made to design bidirectional optical links. In bidirectional (BiDi) optical links, data is transmitted and received over the same optical fiber. Therefore, BiDi optical links are attractive in terms of potentially reducing the number of components (e.g., optical fibers) that are needed to form the link. For this same reason, bidirectional optical links are also attractive in terms of scalability. In addition, many data centers have existing fiber infrastructures that could potentially be used in BiDi links to increase bandwidth without having to add fibers. However, BiDi optical links also present challenges in terms of dealing with optical crosstalk, return loss and signal-to-noise ratio (SNR). For example, higher data rate BiDi optical communications modules (e.g., those operating at speeds greater than 14 Gigabits per second (Gbps)) require greater power margins than modules operating at lower data rates. Consequently, in such modules, it is important to reduce optical losses and sensitivity to optical misalignment. In general, known optics systems used in BiDi optical communications modules are highly sensitive to optical misalignment and result in optical losses that are too great. Accordingly, a need exists for a BiDi optical communications module having an optics system that reduces optical losses while improving tolerance to optical misalignment.